Recovery of wax from lubricating oil stocks



Aug. 5, 1958 H. S. BURK RECOVERY OF WAX FROM LUBRICATING OIL STOCKS FiledFeb. 16, 1954 FuRFu/im {g A M K? INVENTOR.

RECOVERY OF WAXFROM LUBRICATING OIL STOCKS Herbert Stanley Burk, Maplewood, La., assignor to Cit- Con Oil Corporation, Lake Charles, La., a corporation of Delaware Application February 16, 1954, Serial No. 410,472

1 Claim. (Cl. 196-18) This invention relates to the recovery of wax from lubricating oil stocks, and more particularly to a method of increasing the wax percentage in the rafiinate from a solvent extraction process for the refining of mineral lubricating oils.

In the processing of petroleum fractions to produce high V. I. oils from naphthenic, aromatic, or mixed base stocks, resort may be had to solvent extraction to remove from the oil its naphthenic and aromatic constituents to obtain a rafiinate of increased paraflinicity, and an extract containing the undesirable constituents of the charging stock. Solvents useful in such solvent extraction processes include nitrobenzene, sulfur dioxide, and furfural. After separation from the solvent, the raffinate is then dewaxed to' yield a low pourpoint, high V. I. lubricating oil. The extract phase has little value as a lubricant, and is generally used, after separation of the solvent, as a charge stock to a catalytic cracking process, or as a low grade fuel.

I have now found that the extract oil contains considerable amounts of wax, and that the overall wax yield from a given quantity of feed stock can be increased 'by from about 12% to about 20%, depending on the nature of the charge stock, by the process hereinafter described, without any deleterious effect on the lubricating oil produced.

In general, my new process comprises cooling the extract mix from a solvent extraction tower to a temperature low enough to allow the extract to break into two layers, one an oil layer containing most of the wax content of the extract, together with a small quantity of solvent, the other a solvent layer comprising solvent and the more highly aromatic constituents of the extract oil. The oil phase is separated from the solvent layer and is cooled to a temperature between 30 F. and 80 F., in order to separate out the wax in crystalline form, and the mixture is then centrifuged or filtered to recover a wax fraction containing a small amount of oil, and an oil fraction containing some solvent. The latter fraction is combined with the solvent layer from the extract breaking step, and is then sent to the solvent recovery system. The wax fraction is combined with the waxy rafiinate, and the combined streams are sent to the raffinate recovery system in which the raflinate is freed of dissolved solvent, and is dewaxed. It will thus be apparent that by the use of my process the wax recovery may be sub stantially increased without the need for any additional equipment other than a settling tank, a chiller, and a filter or centrifuge.

In order that those skilled in the art may more fully appreciate my invention and the preferred method of carrying it out, it will be more particularly described in connection with the accompanying drawing which is a diagrammatic flow sheet of my new process.

Furfural is continuously introduced through line to the upper part of extraction tower 11, while a petroleum distillate of a suitable viscosity for producing lubricating nited States atent ice oil is introduced to theextraction tower through line 12 at a point near the bottom thereof. The oil will pass upward through the extraction column 11 countercurrently to the furfural, and a raflinate phase is removed from the top of the tower through line 13. Temperatures in the extraction tower 11 are maintained at about 250 F. to 260 F. near the top, and at about 215 F. to 230 F. at the bottom. These temperatures are maintained either by heating means such as steam coils (not shown) located in the tower 11, or by control of the temperature of the furfural and charge oil streams introduced into the tower 11 through lines 10 and 12 respectively.

As the furfural passes downwardly through the tower 11 it will extract from the charge stock undesirable constituents such as aromatics and nahpthenes. An extract phase, comprising furfural and extracted hydrocarbons, is continuously removed from the bottom of the tower 11 through line 14, and is passed through a cooler 15 in which its temperature is reduced to about 120 F., and thence to a settler 16, where the extract phase will break into an oil layer and a solvent layer.

The oil layer, containing wax and a small amount of furfural, is continuously removed from settler 16 and passed through line 17 to a chiller 18 in which its temperature is reduced to from about 30 F. to about F. At this temperature the wax content of the mixture will crystallize. The wax-oil-furfural slurry is then passed through line 19 to a separating means 20, which may be a filter or centrifuge. Oily wax is removed from the separating means 20, is melted, and is passed through line 21 to line 13, where it is mixed with the raffinate stream from extraction tower 11. The wax-enriched raffinate is then passed through conventional solvent recovery and dewaxing steps to recover dissolved furfural, wax, and a high V. I. low pour point oil.

Dewaxed oil and furfural are continuously removed from the separating means 20 via line 22 and are mixed with the solvent layer withdrawn from settler 16 through line 23. The combined streams are then treated by conventional methods for the recovery of furfural, and the solvent free oil is passed to a cracking process or to such other disposal as may be required.

In order to give some idea of the increased yields of wax recovered by processing according to my new method, the following examples are given.

Example I In a commercial operation for'the production of a V. I. lubricating oil of a Saybolt Universal viscosity of at 100 F. furfural may be charged to the extraction tower at the rate of 33,000 barrels per day together with 12,000 barrels per day of a petroleum distillate of suitable viscosity. The temperature at the top of the extraction tower is held at 248 F., and the bottom at 215 F. A waxy raflinate is removed from the top of the tower in a yield, after separation of dissolved furfural, of 54.8% based on the charge oil. This raflinate yielded 8.52% wax, based on the charge oil, when processed according to conventional dewaxing methods, and without employing the present invention. However, when the extract phase from the extraction tower was cooled to F. to break it into an oil layer and a solvent layer, the oil layer separated, cooled to 40 F., filtered to recover an oily wax, and the oily wax was added to the rafiinate fraction, processing of the raffinate yielded 10.18% of fully refined wax, based on the charge oil, a 19.5% increase.

Example II In this operation the charge oil is a distillate suitable for the production of a lubricating oil of 200 viscosity 3 at 100 F. Oil was charged at the rate of 13,500 B. P. D., and furfural at the rate of 33,000 B. P. D. Operating temperature at the top of the tower was 252 F., and at the bottom 229 F. It was found that if the extract phase were settledat 120 F, and the oilphase. separated, cooled to. 73 F., and filtered, that sufficient oily. wax could be recovered to raise the yield of fully refined wax from the:overall operation to 10.94% based on the oil feed, an increase of 12.2% over the 9.75% yield when recovering wax from the raffinate stream alone.

Example III' The charge oil in this case was a distillate of a character suitable to produce a 95 V. I. oil of 350 Sayboldt viscosity at 100 F. Oil was charged at the rate of 11,000 barrels per day, and furfural at the rate of 33,000 B. P. D. Temperature at the top of the extractor was 258' F., and 230 F. at the bottom. Sutficient oily wax was recovered from the oil sprung from the extract mix by settling at 120? R, then cooling to 73 F., and filtering, to raise the overall recovery of fully refined wax to 8.13% based on the feed, as compared to 6.67% when operating according to previous practice, an increase of 21.9%.

It will be observed from the foregoing that by my new process it is possible to substantially increase the wax production from a lubricating oil operation without the necessity of'adding a large amount of additional equipment, since the facilities required for the production of fully refined wax are determined by the volume of oil which they are. required to process, and not by the amount of wax recovered. All that it is necessary to add, to put my new process into operation, is a settler, a cooler, and means to separate an oily wax from the extract oil. In actual production these required facilities can be quickly paid for by the increased volume of wax produced.

Having now described my invention, what is claimed is:

In a solventextraction process in which a petroleum distillate of lubricating viscosity is countercurrently contacted with furfural in an extraction zone at a temperature in excess of 200 F. and in which a waxy raifinate stream of increased paraffinicity over the charge oil and an extract stream comprising undesirable constituents of the charge oil, wax and furfural are separately recovered the improvement which consists in withdrawing the extract stream from countercurrent contact, cooling the extract stream to a temperature of about 120 F., introducing the cooled extract stream into a settling zone wherein upper and lower layers are formed, the upper layer consisting of wax, oil and furfural and the lower layer consisting primarily of oil and furl'ural, withdrawing the upper layer from the settling zone and cooling the same to a temperature of from about 30 F. to about 80 F., introducing the cooled upper layer into a wax separation zone wherein the wax is separated from the oil and solvent, heating the separated wax and mixing the same with the waxy raflinate obtained from the extraction zone, withdrawing cooled oil and solvent after wax separation from the wax separation zone and combining said oil and solvent with the solvent layer withdrawn from the settling zone and further processing the combined stream of rafiinate and wax from the separation zone to recover an oil of lubricating viscosity and a refined wax product.

References Cited in the file of this patent UNITED STATES PATENTS 2,063,369 Diggs et al. Dec. 8, 1936 2,155,644 Evans Apr. 25, 1939 2,248,498 Gross et al. July 8, 1941 2,248,668 Gee -Tuly 8, 1941 

